I have been trying to regress a random effect model, using SAS and have bumped into quite some probs. For some reason, my output displays a standarddeviation of 0 for my covariance matrices. Please find below a specification of my model and my output. My random variable is "bedrijf"(=company).
Can somebody please explain why my covariances do not display a Z-statistic? Thanks in advance!!!
1. My model
proc mixed covtest;
class Bedrijf weekdays ;
Model corwin= weekdays Period1 Period2 Period3 Stir EMP__pos_index_return EMP__neg_index_return Ltir Volatility_Average RMH_pos RMH_neg/solution;
random intercept/subject=bedrijf solution;